Schizophrenia and breast cancer incidence: a systematic review of clinical studies

Studies examining the incidence of breast cancer in schizophrenia patients report increased, reduced or similar incidence compared to the general population. We undertook a systematic review of published data to investigate possible reasons for the variable findings.

The review was conducted according to the recommendations of the Meta-Analysis of Observational Studies in Epidemiology (MOOSE) group [Stroup, D.F., Berlin, J.A., Morton, S.C., Olkin, I., Williamson, G.D., Rennie, D., Moher, D., Becker, B.J., Sipe, T.A., Thacker, S.B. 2000. Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis of Observational Studies in Epidemiology (MOOSE) group. JAMA. 283(15) 2008-2012.]. Methodological issues (Quality Markers) that may explain the variability in the data were identified. Data relating to these issues and the standard incidence rates were extracted. Results were then interpreted in relation to these quality markers.

Data are available from over 6000 female patients with schizophrenia from 13 studies and are reported in comparison to age matched general populations from the relevant country from 1986 to 2008. Although results are widely discrepant ranging from 52% increase in risk to 40% decrease, these data may be understood in terms of cohort age, size and length of follow up as the confounders. Six of 13 studies report an increased or marginally increased incidence of breast cancer. These tend to be studies with more than 100 incident cases of breast cancer, greater than 100,000 person years follow up and older populations.

Breast cancer may be increased in female subjects with schizophrenia. Inconsistencies in study findings may be due to methodological issues such as low statistical power and the age range of cohorts studied. There is no proven risk factor to explain these data; however reduced parity and hyperprolactinaemia may represent putative aetiological factors. Consideration of screening of female patients with schizophrenia for breast cancer is important for clinicians and researchers.